(main collector) sewer. The sewage treatment plants and ...
Transcript of (main collector) sewer. The sewage treatment plants and ...
CHAPTER 3
IMPACT ON SEWER SYSTEM IN AN EARTHQUAKE
Jack Lee
Introduction
The establishment of wastewater treatment plants in the East 3ay has greatly improved the
water environment in the Bay. The 3ay can even be opened for recreational fishing purposes
soon. However, the question posed to us now is whether the facilities will be safe in case of
some natural disaster such as an earthquake. Most sewage treatment plants in the East Bay
were built during the 1950's under the outdated building regulations which were invalidated after
the review of observations from the San Fernando earthquake in 1971. Thus, it is worthwhile to
examine whether or not the East Bay Municipal Utilities District and the City of Berkeley have
done anything to correct the sewage plants and pipelines in preparation for an earthquake in
the City of Berkeley.
It is almost impossible to measure how many preparations are needed to prevent a major
disaster in case of an earthquake in the City of Berkeley. However, the use of a projection of
an earthquake on the Richter Scale of seven along the Hayward fault not only tells us how well
both the EBMUD and City of Berkeley have prepared for a major earthquake, but it also tells us
what is needed to be done. Will the wastewater treatment plants withstand such an earthquake as
that "described above? Should sewer operations cease after destruction of the sewers, what will
be the damages to our health and the marine life in the Bay? To answer all these questions,
we must first understand the whole sewer service system, system components, and then state
their performance in the projected earthquake.
Sewer Service System
The water-borne wastes (called sanitary sewage) are generally transported from the curb
line at the property of origin through the City-owned sewer pipes to the receiving interceptor
(main collector) sewer. The sewage treatment plants and interceptor sewer are owned, operated
and maintained by the EBMUD's Special District one. The interceptor traverses Berkeley from
Albany to Emeryville near the east side of the Eastshore Freeway. The interceptor exists into
Emeryville and ultimately joins the sewage treatment plant on the south side of the Bay 3ridge
toll plaza9 (FIGURE 1).Berkeley has thirteen trunk sewers which carry waste to the interceptor, and two of these
trunks serve the hills of North Berkeley by transporting sewage through Albany (FIGURE 1).
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Special District One (SDO) serves the area which includes the cities of Alameda, Albany,
Berkeley, Emeryville, Oakland, Piedmont, and Stege Sanitary District, which includes El Cerrito,
Kensington and part of Richmond. The SDO is serving an approximate population of 580,000, and
its revenues come from a flat rate charge to all living units which are within the District.
Generators of industrial and commercial waste water are charged in accordance with liquid volume,
weight of solids, and biological oxygen demand of the sewage generated." In 1979, single family
BERKELEYALAMEDA COUNTY
CALIFORNIA
FIGURE 1. Location of the Trunk Sewers
SOURCE: Public Works Department, Berkeley, 1979;
Map from Berkeley Planning Department.
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r
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residences are charged $3.80 per month for sewa^Treaxn^__,n add'i tion, the City of Berkeleyis presently charging single family residences S2.00 per month for transportation of sewage
to the District's interceptor.
Sanitary Sewer System Components
The City of Berkeley has approximately 350 miles of sanitary sewer mains and trunks and
about 190 miles of house laterals (sewer lines which connect to the trunk sewers from all
living units) to be maintained by the Sewer Maintenance Department. The wastewater treatment
plant is composed of pipes ranging in size from 6 inches to 45 inches in diameter (mostly in
metal). The house laterals are 4 inches to 6 inches in diameter, and most of them were con
structed with metal before 1900.1 Most of the sanitary mains are composed of various kinds of
pipelines, such as clay and reinforced concrete.
The reinforced concrete pipe intercepting sewers range from 12 to 108 inches in diameter
and are 21.6 miles in length. Eleven pumping stations lift wastewater in to the interceptors
from the cities of Alameda, Albany, Oakland, and the Stege Sanitary District system; then a
bigger pumping station relifts the flow in the East Oakland section of the south interceptorg
into the wastewater treatment plant.
Causes of Damages to the Sanitary Sewer System Components
The complete shutdown of the wastewater treatment plant due to electric power loss org
earthquake damages has never occurred since its operation started in 1951. The sanitary
sewer plant has two power sources - one from San Francisco and the other from Oakland. In
the past, they have had numerous breakdowns on the pumping stations due to the blockage of pumps
by accumulation of waste materials. However, EBMUD feels such a problem could be resolvedg
quickly without a major cutdown on the plant's service.
The 21.6 mile long interceptor was built with reinforced concrete, and EBMUD expectsg
such design of the intercepting sewers to withstand an earthquake of 6.5 on the Richter Scale.
This hypothesis, however, has never been tested. Because of the location of the interceptor,
which is buried under filled bay mud, I would say liquefaction after an earthquake could have
much impact upon the system.
The mains still in service in the City of Berkeley were constructed of various materials
just around the turn of the century. The speed of replacing the wearing pipes is limited by
the funds available to the City. Thus, numerous old sewers have cracks which have resulted in
a total collapse and have brought a number of damage claims. The number of claims by private
citizens in recent years has gradually increased as shown in FIGURE 2. And since the City
is self-insured, the value of settled claims has also increased parallel to the number of
damage claims filed.
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(
Fiscal Year No. of Claims Value of Claims Number Settled Value Paid
1972-73 2 S 1.050 2 SI.150
1973-74 2 97 1 20
1974-75 3 32.219 3 1.219
1975-76 13 5.366 6 3.2B6
1976—to
(3-22-77)
9 2.261 9 1.200
FIGURE 2. Damage Claims
SOURCE: Public Works Department,Report to City Council, Berkeley, 1977.
The joints between each pipe segment were made of one of the following materials: cement mortar, sulfur
and sand, asphalt and tar, and several compounds containing linseed oil. All of these joint materials are
susceptible to attack by the constituents of sewage. When a joint fails, the annular space between pipe seg
ments becomes a place for entrapment of waste material's, thus causing a blockage. Furthermore, a failed
joint becomes a point of access for infiltrating ground water and for tree roots, which ultimately cause
the failure of the pipe.
Damage Caused by Past Earthquakes and Preparations Made by EBMUD and the City of Berkeley
In the San Fernando earthquake in 1971, most piping systems survived the earthquake with only minor
damage; it was reported that out of the broad areas affected by the earthquake, only a small area would need
acomplete reconstruction of the sewer system.8 Many instances were reported where pipes remained unbroken. However, the most failures reported occurred at the joints. In general, pipes in the ground are
subjected to compression and expansion.5 The measure of the force is Ec, where Eis Young's modulus for the
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material of the pipe and c is the unit of compression and expansion per unit length of the
pipe that is measured. It will generally require tons of force to crush the existing pipe
line, whereas at the joints the pipes are weaker and thus problems often occur there.
It is to nobody's surprise that the sanitary sewer mains in Berkeley are not specifically
designed for major earthquakes. However, flexibility of movement in the pipes and joints has
recently been emphasized seriously by the City of Berkeley. Installation of plastic pipes to
replace the old pipes is gradually in process. Plastic pipes cost less and provide better
flexibility to bend and stretch in case of any earth movement. But how strong an earth move
ment they can withstand has never been tested. "Should they rupture in a major earthquake, we
have to just let the sewage flow on the streets for a couple days," said one source in the
City Engineering Office.
Although the intercepting sewers are built to withstand an earthquake of Richter magnitude
6.5 to 7, the interceptor is susceptible to another source of natural disaster — that is lique
faction of the filled bay mud. One way to prevent such an occurrence is to move the inter
ceptor system inland. However, it will be very uneconomical to provide the labor cost for re
location and to purchase more pumps to lift the constituent, which is normally lifted by
gravity. Another way that seems to be more feasible is to compact the soil underneath the
interceptor so that a chance of liquefaction would not be likely to occur there.
Since there is no limit on how safe is considered safe, I think the City and the EBMUD
have put out every effort to improve the sewer system within their limited resources. In some
areas, however, improvements are needed with immediate attention. FIGURE 3 shows the number of
service calls and repairs in Berkeley. The annual number of service calls has steadily risen
from 1,418 calls in 1970 to 2,058 in 1976 for an average annual increase of 106 calls (about
6.55) per year. Repairs to mains and laterals have increased from 513 in 1970 to 681 in 1976
for an average annual increase in serious repair of 52 per year. This implies that the sewer
net is deteriorating faster than it can be replaced and that the Sewer Maintenance Department
is gradually changing from a prevention maintenance program to one of correction maintenance.
Unless more funding is available to replace the old failing sewers and laterals now, the next
earthquake may result in a more severe disaster to our health by totally destroying the old
sewers and thus causing the overflow of sewage onto the street.
Biological Hazards and Emergency Service in an Earthquake
If a leak or blockage occurs in a sanitary sewer under any house, the wastewater then
saturates the ground gradually. When the water supply pipe is also leaking in a state of lowered
pressure due to the enormous water output by a fire engine to fight fires, the contaminated
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Calendar Service Annual Increase Repairs to Mains
& Laterals
Ann. Increase
.. Reps.Year Calls Service Calls
1970
1971
1418
1554
136
29
513
562
49
71972 1583 569
1973 160825
609
40
1974 1685
77
562-47
1975 1884199
*
61856
1976 2058174
68163
FIGURE 3: Sanitary Sewer Service Calls and Repairs to Mains and Laterals
SOURCE: Public Works Department, Report to City Council, Berkeley, 1977.
Hmisa Lateral
FIGURE 4. Cross-Connectlon of the Water Supply Line and the Sewer (House Lateral).
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2wastewater that saturated the ground may get into the water supply pipe as a result (FIGURE 4).
Such an occurrence is called the "cross connection." Cholera, amebiasis, and ascariasis are
diseases which occur in areas where there are improper sanitary disposal of human feces.
Cross connection 1n sewer and water supply pipe lines and overflow sewage due to the breakdown
of sewers by an earthquake are two possible situations which pose such health hazards to the
public.
In light of the foregoing discussion, it is important to check any breakage in both the
water supply line and sewers with water sampling techniques and available tools after an earth-
ouake. Immediate use of water after an earthquake is not recommended. Furthermore, do not
flush toilets if sewer lines are broken. If water is off, emergency water may be obtained
from the water heater, melted ice cubes and toilet tanks.
In the San Fernando earthquake, the damages to sewer lines were only limited to certain
areas. Thus, the temporary sharing of toilets in areas where no damage occurred is encouraged
even though it may cause inconvenience to the public.
In the event of total destruction of the sewer lines and system, mobile toilets would be
made available to the public by the fire department. However, it is doubtful that such mobile
toilets would reach the disaster area quickly, as the roads would probably be made unavailable
for transportation by the earthquake. A more reliable method is to store a portable emergency
toilet in each house all the time. Such portable toilets not only come in handy in case of an
emergency, but they can also be used on a camping trip where no public toilet is available to
the public.
In addition to the health hazards to the people from the possible rupture of sewer lines
in an earthquake, numerous adverse ecological effects will also be imposed on the marine life
in the Bay by the untreated sewage dumped into the Bay. Contamination of shellfish and elimina
tion of a number of species of fish which can only survive in a higher oxygen water environment
are foreseeable. Thus the disappearance of fish would not only be an economic loss of a food
stock to the whole community, but would also serve as the major cause to upset the ecological
balance of the aquatic community of the Bay.
Conclusion
It is extremely difficult to determine what structures are considered completely safe or
not safe in case of an earthquake. On the other hand, to completely change or upgrade any long
existent structure is quite unfeasible economically. Therefore, the trade-off between money and
safety is often a hectic debate politically. Any improvement on earthquake safety measurement
of various structures 1s vastly dependent on how much funds the citizens are willing to give
up in the trade-off between various public services that they may get and the amount of taxes
that they are required to pay.
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In the City of Berkeley, a rather interesting trend on how to allocate the limited funds to
various public projects has increasingly dominated the funding procedures in recent years; funds
for maintenance of the already existing structures has first priority on available funds, and
then the replacement of any parts of the troublesome structures. The sanitary sewer maintenance
and construction funding in the City of Berkeley is a good example of such a trend (FIGURE 5).
What is bad is that it will shift all the preventative programs (in case of earthquake, the in
stallation of new sewer lines in replacing all old ones) to the corrective programs, which mainly
spend money for fixing the endless problems arising in time.
In order to minimize the damages in case of an earthquake in the City of Berkeley, we have
to have a more comprehensive and preventative program on the whole sewer system. Replacement or
rehabilitation is urgently needed for the 27,000 linear feet of sanitary sewer which have been
identified as high maintenance cost and environmentally deficient by the Public Works Maintenance
Superintendent. Because the new sewers require little or no maintenance and can withstand earth
quakes better as experience indicates, replacement of sanitary sewers in the City of Berkeley
will result in the decrease of maintenance demands, the chances of cross-connection with the
Fiscal Year New FundsReceived
Funds SpentMaintenance
Funds ForReplacement
1971-72 621.005 367432 253573
1972-73 62§092 367453 258,639
1973-74 618,730 448,349 170,381
1974-75 632667 414,575 218,092
1975-76 624,365 463568 160,797
FIGURE 5. Income, Maintenance Expenditures and Sewer Replacement Trends
SOURCE: Public Works Department, Berkeley. 1977.
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water supply lines, and the number of ruptures on the sewer lines during the earthquake.
With the present political structure in our government, opinions and support from the
public are very important in public policy making processes. Public awareness on various issues
is a crucial need in getting an adequate and rational opinion from the general public. There
fore, constantly providing earthquake information and education to the public through periodical
journals and television is most recommended.
REFERENCES CITED
1. Bonwell, J.E., assistant engineer, 1979, oral communication with the Department of PublicWorks on the sewer system in the City of Berkeley.
2. Chanlett, E.T., 1973, Water Resources and Environmental Engineering, S.F., McGraw-Hill,pp. 99-101.
3. McCaull, J., and J. Crossland, 1974, Water Pollution, S.F., Harcourt Brace Jovanovich, Inc.,pp. 127-134.
4. Meade and Small, 1966, Geology of North California, Bulletin 190, California Division ofMines and Geology, S.F., pp. 385-391.
5. Reid, H.F., 1910, The California Earthquake of April 18, 1906, Washington, Carnegie Institution, pp. 39-42.
6. Sewell, G.H., 1975, Environmental Quality Management, flew Jersey, Prentice-Hall, Inc.,pp. 90-101.
7. Steel, E.W., and T.J. McGher, 1979, Water Supply and Sewerage, S.F., McGraw-Hill, pp. 552-593.
8. U.S. Department of Commerce, 1971, San Fernando, California Earthquake of February 9, 1971,Washington, D.C, pp. 753-765 and pp. 828-829.
9. Vossbrink, D., engineer, 1979, oral communication with East Bay Municipal UtilitiesDistrict on the overall sewer system in the Bay Area.
10. Webb, J.S., 1971, Regional Geochemical Reconaissance in Medical Geography, Cannon, H.,and H.C. Hoops, in Environmental Geochemistry in Health and Disease, Geol. Soc. America,Mem. 123, pp. 32^4~2.
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